The purpose of this work is to further our understanding of gene expression during development and disease. The delta-crystallin gene system of the embryonic chick lens is used as a model. This fiscal year we have shown that delta-crystallin is composed of at least three subunits with similar amino acid sequences; that translation of delta-crystallin mRNA in vitro gives all 3 subunits, the rate of synthesis of the subunits is regulated by Na ion and K ion; alteration in the rate of synthesis of the subunits is reflected in a corresponding alteration in the combinations of subunits which assemble into native proteins; alteration in the ratio of synthesis of the delta-crystallin polypeptides does not cause lens opacification, but the development of vacuoles does in cultured embryonic chick lenses; the Na ion-K ion regulation of crystallin synthesis operates during cataractogenesis in the Nakano mouse, which has a hereditary cataract; that delta-crystallin genes are not present in fish, amphibians and mammals, but are present in birds and reptiles; and that delta-crystallin DNA sequences are located on at least four fragments of the EcoR1 digested chick genome.